the salmon, because it can swim against the current and do something unreasonable from the utilitarian standpoint, is a symbol for such contra naturam efforts of man against the flow of nature. It represents the heroic effort against tendencies of laziness
Von Franz argues that the salmon symbolizes the psyche’s counter-natural, heroic striving — contra naturam effort — as well as prophetic wisdom and nourishing vitality drawn from Celtic and Nordic mythology.
, Shadow and Evil in Fairy Tales, 1974thesis